Affinity describes itself as "a growing network of many hundreds of Bible-centred churches and Christian agencies throughout Britain and Ireland". It was founded in 1953 as the British Evangelical Council and in 1981 numbered over 2,000 churches. The organization stagnated in the 1980s following the death of Martyn Lloyd-Jones. The rebranding and relaunch happened in 2004. Affinity provides networking and support to conservative evangelical churches in the United Kingdom and Ireland. There are currently about 1300 church congregations linked to Affinity. The organisation's subtitle is "Church-centred Partnership for Bible-centred Christianity".
The British Evangelical Council focussed, in reaction to the 1967 Keele University conference, "to draw in churches predicated on Scriptural ecumenicity." It was opposed to the World Council of Churches.
Many churches linked with Affinity would consider "Bible-centred Christianity" to be reformed, Calvinist, and non-charismatic, although some in the affiliation would disagree. Thus, many member churches are defined by a rigorous theology, adopting a separatist outlook. They regard churches with differing viewpoints as being in error and refuse to associate with them. For this reason they rarely join the Evangelical Alliance, a similar but larger organisation with a broader membership.
Groups of churches linked to Affinity include the Apostolic Church, the Association of Grace Baptist Churches (South East), the Association of Grace Baptist Churches (East Anglia), the Evangelical Movement of Wales, the Fellowship of Independent Evangelical Churches, the Free Church of Scotland, the Free Church of Scotland (Continuing), the Evangelical Fellowship of Congregational Churches, the Evangelical Presbyterian Church in England and Wales and Ireland and the Evangelical Connexion of the Free Church of England.